Discharge lamp with a reflector and an asymmetrical burner

ABSTRACT

The invention relates to a discharge lamp with a reflector ( 1 ) and an asymmetrical burner, which reflector ( 1 ) comprises at least a reflecting surface ( 3 ) and a hollow reflector neck ( 4 ), while the asymmetrical burner is partly arranged in said hollow reflector neck ( 4 ) without making contact therewith, wherein the shape and the size of the inner contour ( 6 ) of the reflecting surface ( 3 ) of the reflector ( 1 ) corresponds substantially to the contour of the asymmetrical burner, and the asymmetrical burner is centrally located in the reflector ( 1 ).

The invention relates to a discharge lamp with a reflector and anasymmetrical burner, which reflector comprises at least a reflectingsurface and a hollow reflector neck, while the burner is partly arrangedin said hollow reflector neck without making contact therewith.

The light quality is dependent on various parameters, for example theefficiency of the reflector, in the case of a discharge lamp comprisingat least a burner and a reflector. The efficiency of the reflector isinfluenced not only by the nature and quality of its reflecting surface,but also by the reflector geometry. The reflector geometry attuned tothe respective application, i.e. in particular its shape and size, isinextricably interlinked with the nature of the light source and thegeometry thereof.

A light source in the sense of the invention may be, for example, aknown burner of a discharge lamp with a return pole. Such a burner witha return pole, which may be used, for example, in headlights of motorvehicles, has an asymmetrical shape on account of its construction. Ifsuch conventional discharge lamps are used, for example, forapplications in which light is emitted with as low a loss as possibleand is focused on a point or on a defined region, the efficiency of thereflector is dependent inter alia on the size of the reflecting surfacearea. The inner contours of the reflecting surfaces of the relevantknown reflectors, which have a hollow reflector neck, all have acircular shape. The use of such a shape of the inner contour and of anasymmetrical burner renders it impossible to avoid an impairment of thelight quality, here in particular of the light output. If the efficiencyof the reflector has a particular significance, for example inapplications where the light reflected by the reflector is coupled intoan optical waveguide, a significant impairment of the light quality canbe observed, caused by regularly occurring coupling losses. Losses againoccur in the emission of the light from the optical waveguide each time,independently of the former losses, so that the efficiency of thereflector in such an optical waveguide system is one of the substantialdetermining factors for the total efficiency of the system. The use ofsuch an optical waveguide system as a lighting system for motorvehicles, where standardized values must be achieved on a regular basiswith respect to the light quality, necessitates a very exact andexpensive attunement of the optical system components. Optical waveguidesystems for motor vehicles which have at least one light source,comprising at least one discharge lamp with a reflector and anasymmetrical burner, are in the focus of development. These opticalwaveguide systems comprise inter alia a system of optical waveguidecables and optical elements which realize and support the coupling ofthe light into and from the optical waveguide, thus making the lightavailable for the desired application, for example through a headlightof a motor vehicle, in a known manner.

It is an object of the invention to provide a discharge lamp which canbe manufactured in a technologically simple and inexpensive manner,while a required light quality is safeguarded by a good efficiency ofthe reflector.

The object is achieved in that the shape and the size of the innercontour of the reflecting surface of the reflector correspondssubstantially to the contour of the burner, and in that the burner iscentrally located in the reflector.

The invention renders it possible to realize an optimized adaptation ofthe shape and size of the inner contour of the reflecting surface of thereflector to the contour of the burner, in particular taking intoaccount the tolerances necessary for mounting and adjustment of theasymmetrical burner and the reflector, the inner contour of thereflecting surface of the reflector, which merges directly into thereflector neck, being greater than the outer contour of the burner. Thisadaptation according to the invention offers the largest possiblereflecting surface area of the reflector, an adaptation whosesignificance for the total efficiency of the reflector lamp, inparticular in special applications, was ascertained by a plurality oflaboratory experiments and which those skilled in the art have neverbefore conceived or realized. Surprisingly simple means according to theinvention thus provide a reflector lamp which can be used as aneffective light source for optical waveguide systems. The centralarrangement of the burner in the reflector in particular safeguards asimple and accurate adjustment of the focus.

Discharge lamps in the sense of the invention are all known lamp typeswith an asymmetrically shaped burner and a reflector. The asymmetricallyshaped burners are in particular burners of discharge lamps known per sewith return poles.

The reflector according to the invention then comprises usual materialssuch as glass, ceramic material, metal, and/or synthetic resin.

The expression “contour of the burner” is to be understood as being theoutermost contour of the burner within the scope of the invention, i.e.the contour visible in the plan view (x-y plane) of the discharge lampcomprising an asymmetrical burner in the incorporated state, for exampleas shown in FIG. 1.

In a preferred embodiment of the solution according to the invention,the inner contour of the reflecting surface of the reflector issymmetrical with respect to the x-axis and asymmetrical with respect tothe y-axis, while the asymmetrical portion of the burner extends in thedirection of the x-axis after being assembled. Such a shaping of theinner contour of the reflecting surface of the reflector as proposedhere renders it possible to use simple geometric shapes, such assemi-circular arcs and straight lines, while fulfilling the criteriamentioned above, resulting in a satisfactory adaptation of therespective inner contour to the outer contour of the burner in manyapplications, while observing the necessary tolerances.

A further preferred embodiment of the invention in this respect ischaracterized in that the inner contour of the reflecting surface of thereflector has the shape of an ellipse or of a rectangle with roundedcorners.

An alternative embodiment of the invention is characterized in that theinner contour of the reflecting surface of the reflector is adapted tothe contour of the burner such that the surface area of the reflectingsurface reaches a maximum. Such a maximum is reached when very highrequirements are imposed on the mutual agreement of the contours, whileobserving the necessary tolerances. This embodiment is technologicallymore complicated and accordingly requires a correspondingly higherexpenditure in industrial mass manufacture.

The object of the invention is furthermore achieved in that a dischargelamp as claimed in the claims 1 to 4 is used as a light source in anoptical waveguide system which serves as a lighting system for a motorvehicle and which has at least one light source comprising a dischargelamp with a reflector and an asymmetrical burner.

Optical waveguide systems within the scope of the invention comprisebesides a light source at least a system of optical waveguide cables andoptical elements which couple the light into and from the opticalwaveguide and which realize and support the provision of the light tothe envisaged application, for example for lighting purposes, in a knownmanner.

The invention will be explained in more detail below with reference toan embodiment. In the Figure:

FIG. 1 diagrammatically shows a burner with a return pole of a dischargelamp,

FIG. 2 shows a discharge lamp with a return pole in plan view, and

FIG. 3 shows the reflector of the discharge lamp in lateral sectionalview.

FIG. 1 diagrammatically shows a burner 2 with return pole 5 of adischarge lamp, which burner 2 is connected to the return pole 5 withelectrical conduction in a known manner.

FIG. 2 is a plan view of a discharge lamp with a return pole 5 (forexample a xenon lamp) for an optical waveguide system for the headlightof a motor vehicle. The reflector 1 is made of a borosilicate glass hereand has a reflecting surface 3 and a hollow reflector neck 4. The burner2 is centrally located in the reflector 1 by means of a retention device(not shown in FIG. 1) at least partly in the hollow reflector neck 4,without contact between the inner surface of the reflector neck 4 andthe outer surface of the burner 2. A retention device fixes the burner 2in a defined position which safeguards an optimum luminous intensity andfocusing of the reflected light on the focus lying outside the reflector1. In this focus, the reflected light is fed into an optical waveguidecable which is known per se, for example a glass fiber cable, of anoptical waveguide system in a usual manner. The inner contour 6 of thereflecting surface 3 of the reflector 1 is symmetrical with respect tothe x-axis in the x-y plane, and asymmetrical with respect to they-axis. The inner contour 6 of the reflecting surface 3 of the reflector1 is formed by simple geometric shapes, i.e. by two semi-circular arcsof equal size which are interconnected by two parallel straight lines.Given a radius of the semi-circular arcs of approximately fivemillimeters each, the distance of the inner contour 6 from the point ofintersection of the x- and y-axes on the x-axis is approximately fivemillimeters and seven millimeters, respectively.

FIG. 3 shows the reflector of FIG. 2 in a cross-sectional lateral view.A reflector axis 8 extends through the center of the burner 2 in adirection orthogonal to the x-y plane shown in the plan view of FIG. 2.

1. A discharge lamp with a reflector (1) and an asymmetrical burner, which reflector (1) comprises at least a reflecting surface (3) and a hollow reflector neck (4), while the asymmetrical burner is partly arranged in said hollow reflector neck (4) without making contact therewith, characterized in that the shape and the size of the inner contour (6) of the reflecting surface (3) of the reflector (1) has a substantially oval asymmetrical shape corresponding substantially to the contour of the asymmetrical burner and return pole, wherein the shape and size of an inner contour (6) of the reflecting surface is symmetrical in an x-direction and asymmetrical in a y-direction in a cross-sectional view of said hollow reflector neck (4) and orthogonal to the reflector axis (8), and in that the asymmetrical burner is centrally located in the reflector (1), the asymmetry in the y-direction for preventing rotation of the asymmetrical burner in said hollow reflector neck and for increasing a reflective surface area of said hollow reflector neck thereby increasing the light output efficiency.
 2. A discharge lamp as claimed in claim 1, characterized in that the inner contour (6) of the reflecting surface (3) is symmetrical with respect to the x-axis and asymmetrical with respect to the y-axis.
 3. A discharge lamp as claimed in claim 2, characterized in that the inner contour (6) of the reflecting surface (3) has the shape of an ellipse or of a rectangle with rounded corners, or is formed by semicircular arcs and straight lines.
 4. A discharge lamp as claimed in claim 1, characterized in that the inner contour (6) of the reflecting surface (3) is adapted to the contour of the asymmetrical burner such that the surface area of the reflecting surface (3) reaches a maximum. 